United Airlines Flight 826

On December 28, 1997, United Airlines Flight 826 was operated by a Boeing 747-100 flying from New Tokyo International Airport (Narita), Japan to Honolulu International Airport, Hawaii. Two hours into the flight, at an altitude of 31,000 feet (9,400 m), the plane received reports of severe clear-air turbulence in the area and the seat belt sign was turned on.